Standardized age - Length key for east Atlantic and Mediterranean bluefin tuna based on otoliths readings.

Abstract

This paper presents an age-length key (ALK) based on age estimates from otoliths following a recent standardized reading criterion. Sampling of Atlantic bluefin tuna (Thunnus thynnus) otoliths comes from the “Biological and genetic sampling and analysis" (GBYP) project and was complemented with some samples from the Spanish institute of Oceanography. Using 2010 to 2012 data improves length range and monthly sampling coverage. Variability in length at age from ALK seems acceptable and although it was developed from data pooled over three years, the bias is likely to be small. Final age was adjusted to account for the date of capture and the timing of bands formation throughout the year. Monthly formation of edge type, translucent or opaque, was inconclusive and did not allow establishing an annual formation pattern. The confidence interval of the von Bertalanffy growth model curve fitted to ALK data included currently adopted growth function for eastern bluefin stock and western stock function up to age 8. From age 9, this last western function predicts slightly older ages than the present ALK growth model.